The dry cooling of bulk material is old and generally well known. For example, dry coke quenching has been known for over 50 years, and is presently practiced in the Soviet Union using what is known as the Giprokoks system.
Dry cooling of bulk material, particularly materials such as coke, permits recovery of substantial amounts of energy, which, for example, can be utilized in the production of electrical power. If electrical power generation is considered, recovered heat would be equivalent to about 100kw/ton of coke. Additionally, dry cooling in a closed circuit greatly reduces atmospheric pollution which has become associated with such things as the wet quenching of coke. Accordingly, dry cooling of materials provides substantial advantages to the environment and for the recovery of energy. Notwithstanding these advantages, various technical difficulties exist in both the methods and the apparatus for dry cooling.
For the most part, the bulk material supplied to the dry cooling means is supplied on an intermittent basis. For example, in a coking operation, the coke would be pushed and transferred in the incandescent state to the dry cooling system. The coke is supplied after each pushing operation so there is no steady state flow of material into the system, but rather an irregular flow of hot material.
The intermittent supplying of hot material causes considerable heat fluctuation in the temperature of circulating gas. This in turn complicates the construction of the heat exchanger as well as requiring expensive apparatus to obtain and maintain a constant heat supply. For example, the Giprokoks system for dry quenching coke utilizes a pre-chamber within a cooling bunker to store incandescent coke without it being cooled. The stored hot coke enters cooling zone only as a result of coke withdrawal at the discharge end, and, the hot gases escape through a series of ducts leading to an annular channel around the pre-chamber. Also, fluctuation in heat creates problems with respect to the cleaning of dust-laden cooling gas prior to its introduction into a heat exchanger, because the cleaning means must be designed for peak temperature values which the system may experience.
Other problems which have heretofore been associated with systems used in dry cooling relate to the degasification, for example, of hot coke. Problems can arise where the hot materials are cooled by a substantially inert cooling gas when hydrocarbons and carbon monoxide build up within the system and form an explosive mixture. Such an enrichment of carbon monoxide can also occur in installations for calcinated ore caused by the interaction of carbon dioxide with the remaining carbon. If the carbon monoxide gas and hydrogen compounds are present, an increased danger of explosion exists if there is also an enrichment of oxygen present. Similar phenomena occur in installations for cooling sinter material or clinker wherein the changes of chemical compounds of the cooling gas, especially the concentration of sulfur dioxide, can cause difficulties, including, for example, changes in the chemical composition of the sinter or clinker materials.
It is, therefore, an object of the present invention to provide a method and means whereby the temperature of the cooling gas prior to its passage through a heat exchanger is controllably maintained at a substantially constant temperature notwithstanding fluctuation in the heat input to the circuit. It is a further object of the present invention to maintain a constant quantity of cooling gas passing through the heat exchanger, and to continuously condition the cooling gas so as to avoid or maintain within permissible limits any build-up of dangerous gases or changes in the chemical composition of the cooling gas.